Yes, generally it is possible but it depends on the monitor itself and your graphics card. I had two monitors, one actually a tv/monitor at base 50hz and a 1080p 24" ASUS at 60hz, capable of 75hz. With one at 50 and the other at 60, I had issues with dizziness. Depending on your sensitivity to motion, you could cause yourself a lot of issues with different refresh rates unless you turn off the monitor not in primary use. So, running two or more monitors at the SAME time with different hz = bad.
It would be best to have both capable of the same refresh rates and set them accordingly. However, your GPU must be capable of driving both, if for example, they are both 144hz monitors.